Tiny Tuesday: Not ornamental gravel so what is it?

My "Editor" (aka MrsC) thinks this looks a bit like cauliflower, or maybe weird popcorn. I think it looks a bit like ornamental gravel. But it isn't either; the pieces are rather smaller, varying from only 2 to 5 mm across. If you like, take a guess as to what it is - I'll reveal it tomorrow.

Many thanks to jensphotos for looking after Tiny Tuesday - I hope she has as much fun as I did hosting Mono-Monday last month!

(PS The answer is now available on my blip posted tomorrow, here.)